Importing nested categories with HexData

Here are the required fields to import the categories:
title
alias ( same as title )
parent_id ( 0 if main category or the parent category id )
access ( in most of the time set to 1 )
created_time ( not mandatory, but should be there )
created_user_id ( not mandatory, but should be there )
extension ( mostly com_content )
level ( set to 1 for main category, 2 for first child and so on )
published ( set to 1 )

You can import all the categories at once just need to maintain the parent_id and level

What are the minimum field requirements for importing categories with HexData. Also, do I need to import level 1 categories first before level 2 (nested) or can they be imported at once in the same file. Thanks